Re: [Patch] kexec: increase max of kexec segments and use dynamic allocation

[Cong Wang]

On 07/25/10 10:54, Eric W. Biederman wrote:
> huang ying<huang.ying.caritas@xxxxxxxxx>  writes:
>
> > On Thu, Jul 22, 2010 at 3:08 PM, Eric W. Biederman
> > <ebiederm@xxxxxxxxxxxx>  wrote:
> > > Cong Wang<amwang@xxxxxxxxxx>  writes:
> > >
> > > > On 07/22/10 14:28, Eric W. Biederman wrote:
> > > > > Amerigo Wang<amwang@xxxxxxxxxx>    writes:
> > > > >
> > > > > > Currently KEXEC_SEGMENT_MAX is only 16 which is too small for machine with
> > > > > > many memory ranges. Increase this hard limit to 1024 which is reasonably large,
> > > > > > and change ->segment from a static array to a dynamically allocated memory.
> > > > >
> > > > > ???
> > > > >
> > > > > This should be about segments in the executable being loaded.  What
> > > > > executable has one segment for each range of physical memory?
> > > > >
> > > > > Not that generalizing this is a bad idea but with a comment that
> > > > > seems entirely wrong I am wondering what the problem really is.
> > > >
> > > > Ah, I think Neil should explain this.
> > > >
> > > > He made a patch which includes many memory ranges, caused kexec
> > > > fails to load the kernel. Increasing this limit and the corresponding
> > > > one in kexec-tools fixes the problem. His patch is not in upstream
> > > > kexec-tools, AFAIK.
> > > >
> > > > However, even if we don't consider that patch, isn't 16 too small too?
> > >
> > > Generally you just need one physical hunk for the code, maybe a second
> > > for the initrd.
> > >
> > > It is perfectly fine to raise the number of segments as it doesn't
> > > affect the ABI, but it wants a good explanation of what kind of weird
> > > application wants to write to all over memory when it is loaded.
> >
> > kexec can be used to load not only the kernel images, but also more
> > complex images such as hibernation image. So I think it is good to
> > raise the number of segments.
>
> Totally reasonable.
>
> And in all fairness the patch does a good job of raising the limit.
>
> However if that is the goal 1024 is probably a bit low as I believe
> SGI has built machines with that many nodes.  Still after the patch
> under discussion 1024 was only a limit in a header file so it can
> be trivially changed.

So, what is a better number? 2048? :)

Thanks.

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